| Titre | Overflow generation for icing formation: A conceptual model |
| Auteur | Morse, P D |
| Source | 2016 Yellowknife Geoscience Forum, abstract and summary volume; par Irwin, D; Gervais, S D; Terlaky, V; Northwest Territories Geological Survey, Yellowknife Geoscience Forum Abstracts Volume 2016, 2016
p. 48-49 |
| Année | 2016 |
| Séries alt. | Secteur des sciences de la Terre, Contribution externe 20160259 |
| Éditeur | Northwest Territories Geological Survey |a Yellowknife, Canada (Yellowknife, Canada) |
| Réunion | 44th Annual Yellowknife Geoscience Forum; Yellowknife, NT; CA; Novembre 15-17, 2016 |
| Document | publication en série |
| Lang. | anglais |
| Media | papier |
| Formats | pdf |
| Sujets | nappe phréatique; glace |
| |
| Programme | Infrastructures terrestres, Géosciences de changements climatiques |
| Liens | Online - En ligne (complete volume - volume complet, PDF, 1.72 MB)
|
| Résumé | (disponible en anglais seulement)
Icings (also aufeis, naled) form in winter by freezing of water that overflows across frozen surfaces (ground and/or ice). Icing development is most common in,
but is not restricted to, permafrost regions. Source water may seep from the active layer, flow from a spring, emerge from a stream channel, or may be a combination of these inputs. Regardless of the water source, icings occur where lower boundary
conditions of the source aquifer are confining, and where winter conditions are sufficient for the freezing front in the ground to contact the water table and also freeze any overflow. If the freezing front has reached the water table, water can move
to unsaturated unfrozen zones for storage. When the frost table contacts the water table, the closed flow conditions initiate hydrostatic water level rise. If the hydrostatic level rises above the surface (ground or ice), an icing may develop. With
continued downward freezing throughout the winter the water level rises gradually, but the level fluctuates rapidly with short-term air temperature change. Following a cold interval the level declines, but the subsequent rise in air temperature is
followed by a rise in hydrostatic head, and the peak value is above the previous maximum level. Exfiltration (overflow), sometimes accompanied by vertical movement of the ground and ice, coincides with the hydrostatic level peak. The hydrostatic base
value of each succeeding decline increases, as do peak values succeeding rises. Additionally, because of shallow overburdens, large fluctuations in water pressure can occur due to barometric loading, snowfall, icing in the adjacent stream, but may
also be expected due to temperature expansion and contraction of overburden. Here, I suggest that as pressure changes are rapid and are related to air temperature fluctuations, the driving mechanism originates near the surface, and in a manner
analogous to pressure changes observed in lake ice. Thermal contraction cracks that develop on the frozen surface of lakes during cold intervals infill with water from below that freezes in place and increases the mass of ice. Due to this increase,
ice expansion during a warming interval is to a volume greater than the volume preceding contraction. This volumetric increase raises the internal pressure of the ice as the ice sheet is confined (not the water below). On large lakes this results in
pressure ridges. Within closed-flow systems, small water volume changes induce large pressure variations. Thus I hypothesize that within closed-flow systems, infiltration of thermal contraction cracks in ice or frozen saturated ground by water from
the unfrozen zone may reduce the hydrostatic head (water volume) during the cold interval. Subsequent expansion of frozen overburden with greater mass leads to an overall increase in volume and pressure of the upper boundary condition. When the
pressure of the upper boundary increases, so must the pressure of the confined water, leading to exfiltration (i.e. icing) and/or surface uplift (and/or injection ice) where overburden is least resistant. |
| Résumé | (Résumé en langage clair et simple, non publié)
Les glaçages (aussi appelés aufeis ou naled) se forment en hiver par le gel des eaux souterraines qui débordent sur des surfaces gelées (de sol
et/ou de glace). Le développement de glaçage est plus fréquent dans les régions de pergélisol mais ne s'y limite pas. Le débordement est provoqué lorsque la pression de l'eau en profondeur varie en fonction de changements de grande amplitude mais à
court terme dans la température de l'air. Toutefois, le mécanisme reliant ces deux paramètres est méconnu. Nous présentons ici un modèle conceptuel basé sur l'hypothèse que : les changements de pression sont rapides et sont liés aux fluctuations de
température de l'air; le mécanisme d'entraînement provient près de la surface; et le processus est analogue aux changements de pression observés dans la glace de lac. |
| GEOSCAN ID | 299416 |
|
|